Many piliated organisms are known. Such organisms exist in colonies which are predominantly piliated (P+ phase) and those which are predominantly non-piliated (P- phase). The colonies of P+ and P- for each species have a fairly distinctive morphology and those have knowledge of such morphology can, with various degrees of effort and difficulty, separate colonies in the P+ from P- phase.
It has further been shown in the case of P. aeruginosa (Alan M. Levine, PhD. Thesis, University of Pittsburgh, 1979) that in that organism the growth in a particular environment will tend to equilibrate at ratios which depend upon the initial state of the culture and the rate at which one phase is formed from the other, which rates are affected by growth and the media conditions.
It has further been shown that while both piliated and nonpiliated organisms will grow in certain mammalian hosts, the diseases which these organisms cause in these hosts generally occur only or principally when the P+ phase is present. Correlations are known between the prevalence of P+ in an infecting strain and the virulence of the infection. In designing pilic antigens for vaccine purposes it is therefore desirable to grow organisms producing the largest number of pili whereby either a bacterin or pure pilus vaccine can be isolated.
It has been reported, (Yokomizo and Shimizu, Res. Vet. Sci., 27, 15 (1979)) supported by an initial report by Bemis, et al., (J. Clin. Microbiol., 5, 471 (1977)) that piliated organisms of B.bronchiseptica rather than the unpiliated phase are the pathogenic organisms in swine atrophic rhinitis. Bemis, et al. (J.Clin. Microbiol., 15, 1120(1982)) report the preparation of piliated cultures and the separation of the pili therefrom. Heretofore however, there have been no reports on how B.bronchiseptica organisms can be encouraged to grow substantially in the piliated phase to produce cultures which are phase stable after several passages. This phase stability is important since many organisms are reported to lose their virulence after a plurality of passages in laboratory growth media as opposed to growth in their natural hosts.